The present invention is directed to a wheel alignment measurement method and system for vehicle wheels, and in particular to a method and system utilizing imagers, such as cameras, for detecting features of a steerable wheel and determining alignment characteristics of the vehicle wheel.
Caster is a metric in suspension geometry that affects vehicle handling. Caster measures how far forward or rearward, on a flat and horizontal ground surface, the steering axis intersects with the ground relative to the center of the tire's contact patch when the assembly is viewed from the side. Caster is positive when the steering axis intersection with ground is in front of the contact patch center and negative when the intersection is behind the contact patch center. Caster is important in wheel alignment because positive caster imparts steering stability and causes steering return to center after turning. Excessively positive caster can require more power to steer the vehicle. On the other hand, negative caster decreases steering effort but also makes steering less stable, which is thus a tradeoff that is seldom made in modern vehicles due to the prevalence of power steering.
Caster angle is the angle the steering axis makes with vertical direction when viewed from the side of the vehicle. Caster angle is positive when top of the steering axis leans rearward relative to bottom and negative when it leans forward.